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compiler: improve logic when deciding between conjunctions and multi/multi_a #657

Merged
merged 5 commits into from
Mar 12, 2024
Merged

compiler: improve logic when deciding between conjunctions and multi/multi_a #657

merged 5 commits into from
Mar 12, 2024

Commits on Mar 12, 2024

  1. clippy: fix some nits introduced by rust-bitcoin#651

    @apoelstra
    apoelstra committed Mar 12, 2024
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  2. error: remove some unused variants 

    There is more to come, but do a bunch now because it's cathartic.
    @apoelstra
    apoelstra committed Mar 12, 2024
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  3. consolidate some FIXMEs 

    When you grep the codebase for FIXME it's nice if the output isn't
overwhelmed by the same message repeated 20 times.
    @apoelstra
    apoelstra committed Mar 12, 2024
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  4. policy: rename Threshold variant to Thresh 

    This matches the same variant in Terminal, matches the string
serialization "thresh", and will avoid weird compiler errors related to
collisions with the upcoming `Threshold` type.

This will be an annoying API-breaking change, but fortunately(?) this PR
is already breaking the API for thresholds in an annoying way.
    @apoelstra
    apoelstra committed Mar 12, 2024
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  5. compiler: improve logic for deciding between thresholds and ands 

    In our threshold logic we have some special cases to handle multi,
multi_a, and conjunctions. However, we were not choosing between
these special cases correctly. Our logic was roughly that we would
try to use multi_a if all children were pk()s, OR try to use multi
if all children were pk() and there weren't too many, OR try to
use a conjunction if k == n.

The correct logic is: if all children are keys, and there aren't
too many, try to use multi or multi_a. ALSO, if k == n, try to
use a conjunction.

With this fix, the compiler correctly finds that conjunctions are more
efficient than CHECKMULTISIG when k == n and n < 3. When n == 3 the
two cases have equal cost, but it seems to prefer the conjunction. It
also correctly finds that when k == n, it is always more efficient to
use a conjunction than to use CHECKSIGADD.

This change necessitates changing some tests.
    @apoelstra
    apoelstra committed Mar 12, 2024
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